Christian David Hunt. Chapel Hill Approved by: Brian Pietrosimone. Troy Blackburn. Matthew Harkey

Transcription

1 ASSOCIATION BETWEEN QUADRICEPS STRENGTH AND TIBIOFEMORAL CARTILAGE PROTEOGLYCAN DENSITY AT 6 MONTHS FOLLOWING ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION Christian David Hunt A thesis submitted to the Faculty at the University of North Carolina at Chapel Hill in partial fulfillment of the requirements for the degree of Master of Arts in the Exercise and Sports Science Department in the College of Arts and Sciences. Chapel Hill 2017 Approved by: Brian Pietrosimone Troy Blackburn Matthew Harkey

2 2017 Christian David Hunt ALL RIGHTS RESERVED ii

3 ABSTRACT Christian David Hunt: Association between quadriceps strength and tibiofemoral cartilage proteoglycan density at 6 months following Anterior Cruciate ligament reconstruction. (Under the direction of Brian Pietrosimone) Anterior Cruciate ligament (ACL) injury is common in the active population. ACL Reconstruction (ACLR) is used to restore stability and allow for return to activity post-acl injury. A common impairment following ACLR is decreased quadriceps strength in the injured limb, which has been linked to the development of Tibiofemoral Osteoarthritis (OA). Compositional magnetic resonance imaging (MRI) has shown the ability to identify early cartilage changes prior to cartilage structural damage. This preliminary investigation evaluated the association between isometric quadriceps strength and T1rho compositional MRI in weight-bearing regions of tibiofemoral cartilage in 24 subjects at 6 months post-aclr. We found evidence of compositional changes, measured via T1rho relaxation time, with little change to cartilage volume. There was also a statistically significant association between quadriceps strength and T1rho relaxation times for the three regions of the medial femoral condyle, calling for additional research into the interaction of quadriceps and cartilage composition. iii

4 TABLE OF CONTENTS ABSTRACT... III TABLE OF CONTENTS... IV LIST OF TABLES... VII LIST OF FIGURES... VIII LIST OF ABBREVIATIONS... IX CHAPTER I...1 INTRODUCTION...1 SPECIFIC AIMS...5 CLINICAL SIGNIFICANCE...6 CHAPTER II...7 Cartilage Health and Function... 7 ACL Injury Role in Knee OA Development... 9 Damage to Cartilage Bone Marrow Lesion The Meniscus Presence of Inflammatory Mediators QUADRICEPS MUSCLE GROUP AND OA DEVELOPMENT POST-ACLR Quadriceps Strength Post-ACLR Quadriceps Strength Reduction and Biomechanics Quadriceps Strength and OA IMAGING OF KNEE OA iv

5 Radiography Magnetic Resonance Imaging T1rho CHAPTER III METHODS Participants ACLR and Therapeutic Rehabilitation PROCEDURES Quadriceps Strength Measurement Magnetic Resonance Imaging of the Articular Cartilage Magnetic Resonance Acquisition Articular Cartilage Segmentation T1rho Relaxation Time Quantification STATISTICS RESULTS T1rho Segmentation Inter-Rater Reliability Intra-Rater Reliability Differences in T1rho Relaxation Times Cartilage Volume Quadriceps Strength and T1rho Values Post Hoc Analysis DISCUSSION T1rho Relaxation Times Quadriceps Strength Post-ACLR Quadriceps Strength Post-ACLR and Knee Function Quadriceps Strength and Cartilage Health Limitations of Study - Further Development v

6 Conclusion BIBLIOGRAPHY vi

7 LIST OF TABLES Table 1. Subject Demographics Table 2. Inter-Rater Reliability Table 3. Intra-Rater Reliability Table 4. Mean T1rho Values Table 5. Results of Paired Samples T-Test for T1rho Relaxation Times Table 6. Results of Paired Samples T-Test for Cartilage Volume Table 7. Correlations between Quadriceps Strength and T1rho LSI vii

8 LIST OF FIGURES Figure 1. Scatterplot of association between Injured MVIC and T1rho LSI for MFC Figure 2. Scatterplot of association between Injured MVIC and T1rho LSI for MFC Figure 3. Scatterplot of association between Injured MVIC and T1rho LSI for MFC viii

9 LIST OF ABBREVIATIONS ACL ACLR ATT BB BML GAG IKDC JSN KOOS LFC LTC LSI MFC MRI MTC MVIC OA PG ROI Anterior Cruciate Ligament Anterior Cruciate Ligament Reconstruction Anterior Tibial Translation Bone Bruise Bone Marrow Lesion Glycosaminoglycans International Knee Documentation Committee Joint Space Narrowing Knee Injury and Osteoarthritis Score Lateral Femoral Condyle Lateral Tibia Condyle Limb Symmetry Index Medial Femoral Condyle Magnetic Resonance Imaging Lateral Tibia Condyle Maximal Voluntary Isometric Contraction Osteoarthritis Proteoglycans Region of Interest ix

10 CHAPTER I Introduction Anterior cruciate ligament (ACL) injury accounts for 50% of all knee injuries in the athletic population 1. Additionally, ACL injuries occur generally in a younger and more active population, with 18 years of age being the median age of ACL injured patients 2. Surgical ACL reconstruction (ACLR) is often used to improve static knee stability and return patients to physical activity 3,4. Treatment of ACL injury accounts for over 1 billion dollars in associated costs in the United States annually 1. Despite modern advancements in ACLR techniques and improved knowledge and application of rehabilitation and strengthening programs, those who have torn their ACL are still at an increased risk of either tearing the graft in the ACLR limb or the ACL in the contralateral limb 5. While the re-injury rate is alarming, the long-term consequences of ACL injury and ACLR, specifically the risk of developing tibiofemoral osteoarthritis(oa), add additional cause for concern The development of OA results in increased medical costs annually of over 12,200 dollars 11, and currently does not have a functional cure 12. Those who have experienced ACLR are both more likely to develop OA 13 and develop it sooner than those who have not In a systematic review of the literature, 36% (286/795) of subjects who experienced ACLR demonstrated evidence of radiographic knee 1

11 osteoarthritis within the first decade of ACLR, 48% (702/1468) demonstrated OA in the second decade, and 42% (100/237) demonstrated OA in the third decade 7. Currently, the pathogenesis related to knee OA onset is unknown 8, yet it has been suggested that a combination of acute and chronic factors contribute to its development post-aclr 17. The factors that have been suggested to contribute to the acute development of knee OA are varied: initial damage to the cartilage 18, damage to the meniscus at the initial time of injury 19, and alterations in tissue composition due to the presence of inflammatory mediators 8. Some chronic contributors to the development of knee OA are altered joint proprioception 20 and reduced strength of the quadriceps musculature 21, both of which combine to alter the kinematics of the knee during walking gait. Cartilage is influenced by the loads placed upon it 22, and the preservation of functional joint biomechanics following ACLR is paramount to maintaining long-term joint health 23. Individuals with ACLR demonstrate altered joint kinematics via smaller knee flexion angles 24, as well as greater tibial external rotation during knee flexion 25,26 and greater anterior tibial translation 27 compared to healthy controls in walking gait. There are also alterations in knee motions via changes to joint kinetics such as changes in the knee flexion moment{hart, 2015 #148}, and knee adduction moment 22,28 during more dynamic motions such as the single leg hop, when compared to uninjured controls. These alterations in joint kinematics result in subsequent alterations in the patterning of load experienced by the tibiofemoral cartilage 25. 2

12 One of the most vital components to the preservation of knee kinetics is the strength of the quadriceps muscle group. Quadriceps strength contributes to the balancing of forces acting on the knee 29 by transferring forces through the knee 21. Quadriceps strength is markedly reduced post-acl injury and surgical reconstruction These reductions in knee extension strength contribute to the higher mechanical forces experienced by the tibiofemoral joint 34,35 and cartilage degradation within the knee. The presence of a low quadriceps to hamstring ratio (r=0.6) and lower quadriceps strength index (r=0.39) 6 months post-aclr have been associated with the development of knee OA 36. Finally, deficits in quadriceps strength are associated with increased joint space narrowing(jsn), an indicator of knee OA, at 4 years post-aclr 37. In the case of these studies, the authors called for additional research to evaluate quadriceps strength in conjunction with quantifiable measures of knee tibiofemoral cartilage health in order to better understand the pathogenesis of posttraumatic knee OA. In the identification and diagnosis of knee OA, the ability to obtain accurate imaging of knee cartilage may allow for the development of appropriate interventions to ensure a higher quality of life in the patient post-surgery Radiographs are currently used as a method to diagnosis knee OA. However, this technique is limited as radiography depends on indirect measures of cartilage via quantification of the joint space width or the presence of osteophyte formation due to its inability to view cartilage directly 41. Magnetic resonance imaging (MRI) is more sensitive for identifying structural damage to knee cartilage 42. Structural MRI has been used to identify damage to the cartilage by evaluating cartilage thickness over time through 3

13 consecutive imaging sessions. It is important to consider, however, that at the earliest stages of knee OA, there are alterations in cartilage composition prior to changes in the overall thickness of the cartilage 43. Structural MRI is unable to capture these early cartilage alterations, and thus is limited in its capacity to capture the earliest stages of OA. These limitations in current conventional techniques call for procedures capable of identifying alterations in cartilage at a compositional level 44. T1rho MRI imaging is emerging as a technique that enables researchers to quantify changes in knee cartilage before structural deformations occur 25. T1rho evaluates movement of water molecules as they progress through the hyaline cartilage of the knee, measured in milliseconds (ms). Healthy cartilage consists of a high quantity of proteoglycans (PGs) and glycosaminoglycans (GAGs). These cellular constituents of cartilage influence the movement of water molecules through the cartilage tissue. In cartilage that has experienced compositional damage, the densities of PGs and GAGs are reduced, resulting in a more rapid movement of water within the cartilage and consequently an elevated T1rho relaxation time 45. The ability of T1rho imaging to provide information regarding proteoglycan density permits it to be used to identify cartilage that is in a pre-oa state. Early identification of modifiable contributing factors to the development of OA will aid clinicians in the selection of interventions that could prevent OA development. Quadriceps weakness has previously been reported as a contributor to OA development 35, but the relationship between muscle strength and early compositional changes to cartilage has only recently begun to be explored. T1rho 4

14 MRI is a current imaging technique that reflects proteoglycan density in tibiofemoral cartilage 46 and proteoglycan depletion is an early sign of OA development. There currently is a lack of research into the relationship between quadriceps strength and proteoglycan density. Therefore, identifying the association between quadriceps strength and cartilage T1rho relaxation values post-aclr would help build evidence of the role quadriceps strength has on very early compositional changes in a young population at risk for posttraumatic OA following ACLR. The presence of a strong association would contribute to the understanding of the role that quadriceps strength has on early changes to cartilage composition post-aclr, and drive increased emphasis to the improvement of strength post-aclr to facilitate long-term joint health. Specific Aims o Specific Aim 1: Compare T1rho relaxation times and cartilage volume between the injured and uninjured limbs at 6 months post-aclr in 6 weightbearing regions of interest (ROI) of the tibia and femur. Hypothesis: ACL injured limbs will demonstrate a higher mean T1rho relaxation time than the uninjured limbs, while exhibiting no difference in cartilage volume. o Specific Aim 2: Identify the magnitude and direction of the association between quadriceps strength and mean T1rho relaxation times in the injured limb normalized to the uninjured limb (T1rho LSI). 5

15 Hypothesis 1: Lower quadriceps strength of the injured limb will be moderately associated with elevated T1rho LSI in the weight bearing ROI of the femur and the tibia. Hypothesis 2: Lower quadriceps strength LSI will be moderately correlated with elevated T1rho LSI. Clinical significance Determination of the association between T1rho relaxation times and quadriceps isometric strength will add to the body of evidence highlighting the role of quadriceps muscle strength in cartilage health post-aclr. If a moderate negative correlation exists between quadriceps strength and the T1rho relaxation times, added emphasis should be placed on regaining quadriceps strength early following ACLR and maintain quadriceps strength following ACLR in order to promote longterm cartilage health and decrease the risk of developing OA. 6

16 CHAPTER II Cartilage Health and Function Any discussion of tibiofemoral OA must begin with having a prior understanding of cartilage structure. The hyaline cartilage that comprises the tibiofemoral joint is generally between 3 to 4mm thick and covers the regions of the medial and lateral femoral condyles, as well as the medial and lateral tibial plateaus 39. The tissue composition is 65% to 85% water, with the remaining weight comprising of an extracellular matrix consisting of type II collagen (15-20%), proteoglycans (3-10%) 39, and cartilage-producing chondrocytes (less than 10%) 47. The structural organization of cartilage consists of various layers of tissue through a complex extracellular matrix 48. The superficial layer of cartilage is arranged as to create a low friction surface to promote the arthrokinetic motions of roll and glide. This layer consists of thin elongated chondrocytes with fibers resting parallel to the surface and is densely packed with type II collagen 47. This results in cartilage that is strong, but has a limited capacity to heal itself due to its avascular nature 47. If damage is sustained by the superficial layer, the chondrocytes will lay down type I cartilage or a fibrocartilaginous scar tissue which lacks the load bearing capacity of the original type II collagen 49. 7

17 The second, or transitional layer consists of larger diameter fibers that are randomly dispersed through the tissue matrix. It has chondrocytes which are more metabolically active, which provide an increased capacity for collagen remodeling and healing 50. The deep zone contains still larger chondrocyte fibers that are oriented vertically relative to the underlying bone and articular surface. This zone s high proteoglycan and water content lend this layer to be better suited to resist compressive forces 47. Proteoglycans are a vital constituent of cartilage health that are synthesized by the chondrocytes, and consist of glycosaminoglycans attached to a protein core. Proteoglycans are hydrophilic, which enables them to draw water from the extracellular matrix. This generates a swelling pressure which serves to counteract the pressure experienced by the cartilage during weight-bearing that drives water out of the extracellular matrix 51. Due to this interaction, the distribution of proteoglycans in the tibiofemoral cartilage is not homogenous throughout the tissue 48. Specifically, the portions of the cartilage that are subject to greater compression stress show higher content of proteoglycans, which makes these areas stiffer and better able to resist deformation 52. The density of proteoglycans is found to be almost 34% higher in the weight-bearing zones of the tibiofemoral cartilage relative to non-weight-bearing sections 53. With proteoglycans being vital to the healthy structure of cartilage, their damage and subsequent depletion has highly deleterious effects on cartilage integrity and stiffness 49,54. A study conducted by Saar et al. found that human cartilage deforms at 8

18 significantly lower levels of compression in proteoglycan-depleted cartilage than in healthy cartilage 51. ACL Injury Role in Knee OA Development Anterior cruciate ligament (ACL) injury commonly occurs within the athletic population 1. Oftentimes, reconstructive surgery (ACLR) is used in an attempt to recoup stability in the knee joint in the younger or more physically active patient population 55. However, a recent review of the literature found that patients who had received ACLR were diagnosed with an increased prevalence of tibiofemoral osteoarthritis (OA): 44% of those who received ACLR as opposed to the 37% of those who did not receive surgery 7. This indicates that while ACLR is promoted as a procedure to help provide ligamentous stability and help the athlete return to previous activity levels, ACLR does not provide protection against concurrent slowdeveloping pathologies. The odds ratio for developing OA post-acl surgery is 4.2 (3.11,5.99) 56 to 7.0 ( ) 57. This means that those who have had an ACL injury and concomitant surgery are 4 to 7 times more likely to develop knee OA than healthy individuals. With regards to the timing of knee OA, there has traditionally been a noted range of time of to years between ACLR surgery and the consequent diagnosis of OA. In the research conducted by Nordenvall et al. evidence of radiographic tibiofemoral OA was found in 10% of patients post-aclr. In a study conducted by Von Porat et al., 78% of patients had noted structural changes evidenced by radiograph in the respective injured knee within 14 years of surgery. Of those with 9

19 structural changes, 41% had structural deformities severe enough to qualify them to be diagnosed with OA 58. The development of cartilage degeneration after ACLR is initiated and driven by a variety of factors 17. One study evaluated 62 subjects after ACLR surgery and evaluated for 10 different variables to identify characteristics that could be utilized to identify those who are at risk for post-traumatic tibiofemoral OA. Of the 10, the variables that showed the strongest discriminators for developing OA were the presence of meniscus damage/meniscectomy (r= 0.72) receiving chondral damage in the initial injury (r=0.41) and the presence of a weak quadriceps muscle group (r=0.39) 36. Another strong contributor to the development of post-traumatic OA is the presence and severity of bone marrow lesions 19,59. Damage to Cartilage Injuries to the ACL are generally classified as pertaining to one of two categories due to their mechanism, contact or noncontact, with almost 70% of the injuries seen being attributed to a noncontact mechanism 55. During noncontact injury, the patient is generally cutting, jumping, or pivoting on one leg. The vertical loading from the jump results in a force of approximately 6 times the patient s bodyweight that is experienced by the tibiofemoral joint 60. At impact, the tibiofemoral cartilage is subjected to a high degree of stress by the compressive and shear loads placed upon it, resulting in damage to the cartilage as well as the ACL 9. Injuries to the tibial plateau have been found to be significantly dependent on the loading position of the knee at time of injury. Levine et al., while observing cadaveric knees 10

20 placed under load, found that that while no relationship existed between stabilizing structures of the knee joint and loading patterns for ACL injury, tibial plateau injury patterns were significantly dependent on their respective loading condition for cartilage damage 61. This finding was corroborated by an observational analysis completed by Potter et al. This study observed the damage sustained by the cartilage in a ACL injury over the course of 11 years using a cohort of 40 subjects who had experienced an isolated ACL tear. 2 subjects suffered a subsequent ACL tear in the course of the study, bringing the total knees observed to 42 knees. Of the 42 knees injured in the course of the study, all of the patients had visible damage to the cartilage along the lateral tibial plateau at the time of initial injury as visualized by MRI 9. An arthroscopic study done by Hirose et al., found that in 23 subjects who had a traumatic ACL tear, 15 of them experienced damage to the articular cartilage. Of those who experienced damage, 8 had damage isolated to the medial femoral condyle (MFC), 5 had damage to both medial and lateral femoral condyles(lfc), and 2 had damage to the MFC, LFC and lateral tibial plateaus (LTP) 62. Cartilage is a dynamic structure whose thickness 63 and composition 64 are subject to change. In a study by Frobell et al., 61 subjects had MRI measurements of their tibiofemoral cartilage over the course of 2 years at the 3, 6, 12, and 12 month post-acl injury time points. Frobell found that cartilage thickened over central medial aspect of femur (+2.7% percentage change) and significantly thinned in posterior femur in the medial (-2.6% change) lateral zones (-2.6% change) 65. This change in cartilage thickness profile is due to the altered loads placed upon the knee and associated up or down regulation of chondrocyte metabolism 23,66. 11

21 Bone Marrow Lesion In an ACL injury, not only is the cartilage acutely damaged but there is the damage to the underlying subchondral bone 61. This is associated with a pattern of bruising which extends from the cortical layer of bone into the deeper tissue, described in the literature as a bone bruise (BB) or bone marrow lesion (BML). BML are found in conjunction with an ACL injury in 30-70% of the instances 67. BML will appear on an MRI as increased signal intensity in the subchondral bone near the osteochondral junction 68. BMLs are more often found on the lateral side of the knee due to the increased abduction moment experienced by the knee in noncontact ACL injuries The presence of BML have been seen at the time of injury 43,59,63,65,72,73 and will generally decrease in size over time 43. In a study by Frobell in 2011, at diagnosis of ACL tear, 95% of the subject s knees presented with posttraumatic BML in the lateral aspect of the tibial plateau with a mean volume 12.9 ml. Additionally, 77% of the subjects demonstrated the presence of BML on lateral aspect of femoral condyle with a mean volume of 6.9 ml. At 2 years post-injury, there was a complete resolution of BML for 54 of the knees in the lateral compartment of tibia and for 44 of the knees in the lateral portion of the femur. During this time however, 21 knees developed new lesions post-surgery over the lateral portion of the femur and the tibia 65. The presence of BML is relevant because the size of bone marrow edema pattern at baseline has been found to be significantly associated with increased cartilage loss at year 1 (p=0.001), year 2 (p=0.008) and year 3 (p=0.039) postinjury 9. 12

22 The Meniscus The meniscus contributes to filling the joint space between the femur and the tibia. This structure consists of a C-shaped medial meniscus and an O-shaped lateral meniscus, each consisting of an anterior, central, and posterior horn. They are split into 2 zones: with the larger inner zone comprised primarily of type II collagen and being unvascularized, with the outer zone being smaller, vascularized, and comprised of type I collagen 74. The menisci serve two roles in relationship to a healthy knee joint: they serve to provide stability to the tibiofemoral joint by increasing surface congruity between the convex femur and the flat tibia and they also serve to help distribute forces in the knee to help protect the articular cartilage. The force distribution of the meniscus ranges between 44% and 78% of the vertical compression load. Additionally, 61% to 81% of posterior shear force is attenuated by the meniscus as the knee moves through flexion 75. Damage to the meniscus is often found in conjunction with an acute ACL tear 2. This happens due to the mechanism of injury that damaged the ACL ligament and articular cartilage Damage to the meniscus, regardless if it occurs in the medial or lateral portions; results in increased compression of the tibiofemoral joint space, as well increase in the anterior/posterior shear forces experienced by the knee joint 78,79. After damage to the meniscus has been sustained, the likelihood of damaging the hyaline cartilage rises to as high as 80% in the section of the knee associated with the meniscus tear 76,80 or an odds ratio of

23 Presence of Inflammatory Mediators Traditionally, knee osteoarthritis has been viewed as a mechanically driven pathology 82. After ACL injury, mechanical changes to the loads placed upon the knee cartilage do not completely explain the variability in time from injury to diagnosis of knee OA. Damage to the cruciate ligaments, joint capsule, and other synovial tissue cause a metabolic cascade of inflammatory mediators. This has led to research of looking at chemical biomarkers in an attempt to identify possible factors that contribute to the increased damage of cartilage and incidence of OA 72. The cartilage building block of proteoglycans are structured with a protein core with glycosaminoglycan (GAG) side chains. These have been found to be sensitive to inflammatory cytokines which accelerate the degradation of PGs and GAG s in cartilage to a significant extent 83,84. One particular inflammatory mediator that has been shown to cause cartilage degradation is the presence of Intra-articular Interleukin (IL) This cytokine triggers the release of release of matrix metalloproteinases (MMP) 86. This collection of cytokines affect the cartilage in two manners; primarily by breaking the GAG chains 87, and secondarily by activating procolleganase which functions to catabolize the cartilaginous matrix 88. Quadriceps Muscle Group and OA development Post-ACLR In order to maintain a healthy joint, there needs to be a balance between the internal and external forces that the joint experiences at any given point in the sagittal and frontal plane movements 89. The quadriceps muscle group achieves this 14

24 balance by co-contracting with the hamstrings during closed kinetic chain tasks in order to help promote joint congruency and stability 90. Quadriceps Strength Post-ACLR While there has been some argument regarding the role of the of the quadriceps in the initial noncontact ACL injury 91, there is widespread recognition that the strength of the quadriceps muscle is drastically reduced post-acl injury and subsequent surgery 92. These deficits are present as soon as at 1 month post- ACLR 30. In the study previously mentioned, isometric quadriceps strength was compared between injured and uninjured control groups at various time-points after ACLR. In this study, the average torque produced by injured knees was 83 Nm, while the corresponding limb in uninjured control subjects generated 210 Nm 30. This lack of strength is not isolated to being found shortly after injury, with deficits being observed at 3-4 years or more post-surgery 32,93. Deficits in quadriceps strength have been found to be predictive of limitations in self-reported function post-aclr 31. One study viewed the relationship between quadriceps strength and different functional tests at 6 months post-surgery. The authors found ACLR patients who reported low levels of knee function, measured by having a mean IKDC (International Knee Documentation Committee) survey score of 74.7, also presented with a diminished quadriceps strength LSI of 0.80 between the injured and healthy knees. This is a noted difference from those reported higher levels of function via a mean IKDC score of 92, who demonstrated a LSI of

25 While knee extensor strength has been recognized for its role in the function of healthy knees, recent reviews of the literature found that there is no universal standard for identifying when an athlete is cleared to return to play post-aclr 95,96. In a review conducted by Lynch et al., the authors suggested that ACLR limbs need to demonstrate quadriceps strength between 85% and 95% of the uninjured limb in order to be termed a successful outcome. In more recent years, more functional and quantifiable measures of quadriceps strength have been used to evaluate quadriceps strength post-aclr. In a study by Kuenze et al., 22 ACLR subjects at 31 months post-surgery were matched with 24 uninjured controls. The variable of interest was the maximal voluntary isometric contraction (MVIC) of the quadriceps muscle group normalized to body mass (Nm/Kg) as well as the quadriceps strength limb symmetry index (LSI) (injured/uninjured). Those who had experienced ACLR were found to have a MVIC of 2.46(Nm/kg) with an LSI of 0.85 between the injured and uninjured knees, as opposed to a 2.72(Nm/kg) and LSI of 0.97 for the control group. Using a receiver-operator characteristic (ROC) curve, a clinical threshold was suggested to maximize patient reported outcomes of increased functionality and decreased pain and limitation post-aclr. The identified threshold was an MVIC of 3.0(Nm/kg) and a LSI strength index of Quadriceps Strength Reduction and Biomechanics The quadriceps muscle group is one of the largest and strongest muscle groups in the leg 98. This being the case, quadriceps strength is invaluable to healthy knee joint mechanics by contributing to the control of forces acting on the knee 99. In 16

26 the study previously mentioned 99, quadriceps strength was significantly correlated with the peak knee flexion angle during the first 50% of stance phase in walking gait. Greater knee flexion angles place higher demand on quadriceps, noted by the correlation between knee flexion angle and flexion moment (r=0.66) 99. Strength losses post-aclr surgery have a net result of changing the kinematics of the knee joint 100. In the afore-mentioned study, subjects who were at minimum 12 weeks post-alr were divided into operationally weak and strong groups dependent on the quadriceps LSI, 0.80 and 0.90 respectively. Subjects in the weak group demonstrated showed diminished knee angle (20.99 degrees) at peak flexion in walking gait when compared to uninjured controls (26.54). Subjects classified as strong demonstrated no significant difference from uninjured controls 100. Decreased knee flexion angles result in decreased surface area of the tibiofemoral cartilage which experience weight-bearing, resulting in higher loads placed upon the weight-bearing cartilage 101. Diminished quadriceps strength is also associated with increased variance in knee angle 24, resulting in changes of the portions of the cartilage that experience the higher degrees of load 23. These changes in forces experienced by the knee contribute to the continued development of knee OA post-aclr 34,35. Quadriceps Strength and OA Quadriceps strength deficits are a common development post-aclr 92 as well as being found in conjunction with knee OA 102,103. This results in questions regarding the nature of the relationship between quadriceps strength and the role that it plays 17

27 in OA pathogenesis and development. Currently the literature is conflicting regarding the presence and nature of this relationship. Previous studies viewing the association between radiographic OA and quadriceps strength have found results ranging from there being no relationship between the two 104, no protective effect of strength to incidence of OA- but there being a reported decrease in pain (p<0.002) and increased function as strength improved (p<0.0001) 105, to there being a protective effect for increased quadriceps strength against patellofemoral cartilage loss 106, to increased strength protecting against the progression of tibiofemoral OA 35. This spectrum is due to the fact that many previous studies defined OA as being able to be seen and captured by radiograph. In the review by Segal et al., it was noted that while research which viewed the relationship between strength of the quadriceps muscle group and radiographic changes to cartilage found no association between the two; research which evaluated quadriceps strength in conjunction with the developmental stages of OA found the inverse to be true 34, suggesting that quadriceps strength could be more impactful on cartilage health than previous research would have suggested. In all cases, authors called for more research using techniques more sensitive then radiography in order to better identify the relationship and role of quadriceps strength and the early development of knee OA 21,34,107. Imaging of Knee OA Diagnosis of the entity of post-traumatic osteoarthritis can be very difficult due to the lack of readily available and simple orthopedic testing aside from monitoring a patient s history and pain 108. The use of diagnostic imaging in this case is therefore 18

28 vital to identify the scope and severity of cartilage damage 109. Due to the long-term implications of being diagnosed with OA, the more rapid diagnosis and location of degenerative changes in the hyaline cartilage allows for more rapid treatment and improved strategies to maximize patient outcomes by preventing the development of knee OA. Radiography Radiography is a classic staple for the development of knee OA due its ease of use and cost-effective nature. It is important to note however, that when viewing cartilaginous structures that radiography is limited. Due to a lack of ability to capture cartilage directly, radiography relies on tracking cartilage health through indirect measures- namely the presence and development of osteophytes and the narrowing of the tibiofemoral joint space, using systems such as the Kellgren-Lawrence Grading Scale 110. The presence of marginal osteophytes in the tibiofemoral joint space has been demonstrated to be a measure used to identify knee OA. A meta-analysis demonstrated that 20% of those who have sustained an ACL injury demonstrate moderate to severe changes in the cartilage as measured by radiography as opposed to 4.9% in the control group- representing a 4x increase in risk 111 to the cartilage post-acl injury. The use of radiography however has been shown to be not particularly sensitive to evaluating early changes in cartilage degeneration. In a study by Kijowski et al., 125 patients with tibiofemoral OA were evaluated via radiography and had their OA scores compared with values gained by arthroscopy. 19

29 The sensitivity of measuring osteophytes and OA progression in the medial compartment of the knee was 67% in identifying a true positive, and a specificity of 73% in identifying a true negative. The values of the lateral compartment were less sensitive, 49%, however it was more specific, 81%. This study also reviewed the sensitivity and specificity of measuring for the presence of joint space narrowing (JSN) in the medial and lateral compartments of the tibiofemoral joint. While the specificity, or true positive, of JSN was low for the medial (46%) and lateral (7%) compartments, the specificity was very high for both compartments (95%) and (100%) respectively. This means that by the time that JSN is found on radiography, OA has already developed in the evaluated limb 112. It is important to note that in the time that there is sufficient change in osteophyte formation and JSN to be indicative for knee OA, there has been a loss of 11%-13% in cartilage volume as measured by MRI 113. As a result, more sensitive means of imaging are needed to identify early changes to cartilage structure and health than are offered via radiography. Magnetic Resonance Imaging The use of magnetic resonance imaging has been increasing in recent years as related to knee OA identification and tracking due to its multiplanar imaging, tissue contract, and lack of invasiveness. It is used clinically when attempting to visualize tissue that is not readily visible on radiographs; such as the cruciate ligaments, meniscus, and knee hyaline cartilage 43. Clinical magnetic resonance imaging (MRI) will oftentimes use a fat-suppressed model to the increase contrast 20

30 between tissues to be better able to identify defects in the cartilage 38. It is important to note that the use of MRI serves to provide a snapshot of the body segment of interest at any given moment and serial images need to be taken to track changes over time, particularly in the case of knee OA where changes can be insidious 9,43,65,114. While tracking changes to the knee cartilage in OA, it is important to have a grading system in order to classify and the levels of damage. One of the best has shown to be the whole organ magnetic resonance imaging score (WORMS). A given knee is classified by the thickness of the cartilage and its corresponding signal. Healthy, undamaged cartilage is scored as a 0, signifying normal thickness and signal. Early chondral defects of 1 signify normal cartilage thickness but with an increased signal. The score of 2 identifies a partial thickness focal defect that is less than 1 cm in width. A score of 3 signifies the presence of either multiple areas of partial thickness defects mixed with areas of normal thickness or a grade 2 defect wider than 1 cm but less than 75% of the region. For a knee to be scored as a 4, there needs to be diffuse regional partial thickness loss that extends for more than 75% of the cartilage. To score a 5 identifies multiple areas of full thickness loss or a grade 2.5 lesion wider than 1 cm but less then 75% of the region. Finally, scoring 6 signals the presence of full thickness loss of the cartilage. The normal WORMS paradigm has been shown to be a reliable measure for grading cartilage health

31 T1rho Recent developments in imaging have brought about the creation of quantitative MRI techniques 39,40. These allow the clinician to quantifiably measure components of the tissue of interest 45. Regarding the study of OA, the technique of T1rho has been found to be able to accurately measure proteoglycan density via measuring the motion interaction between water and the local macromolecule environment 116,117. This provides the clinician the capability to identify the breakdown of cartilage by measuring proteoglycan (PG) depletion in the cartilage 38. PG depletion is identified when the values for a particular region of interest are elevated as the lack of PGs result in a decrease of free water and a resulting increase in T1rho mean relaxation time 118. The use of T1rho to identify cartilage health post-aclr has been shown to be effective. T1rho imaging has able to identify PG health at injury baseline and reductions of PG density as recently as 6 to 12 months post-aclr 46,119. This was evidenced in a study completed by Theologis et al., in which 18 subjects had T1rho imaging done in order to evaluate the health of the tibiofemoral cartilage at the 12 and 16 months post-aclr. Each patients knee was divided sagittally into medial and lateral portions, each of which was further divided into 8 different regions of interest (ROI); 5 on the femur, 3 on the tibia. The results showed evidence of changes to the T1rho relaxation times in the weight-bearing zone of the medial tibial plateau and femoral condyle at months post-aclr, with no notable difference in cartilage thickness between injured and healthy knees. The opposite was found to be true in the lateral compartment, with the T1rho was unchanged, but the thickness 22

32 profiles for the lateral femoral condyle and tibial plateau were significantly thinner. Sub-compartment analysis of the medial tibia revealed the weight-bearing region had greater T1rho and thinner cartilage compared to the uninjured knee. The medial femoral cartilage s most anterior compartment and weight-bearing regions demonstrated greater T1rho relaxation times in the injured knee when compared to the same region in the uninjured knee 80. The sensitivity of T1ro to identifying pre-osteoarthritic changes has been well documented 120. Research done by Gubta et al., found T1rho presented with elevated values for the whole knee when compared with what was quantified as normal cartilage via arthroscopy and traditional magnetic resonance imaging at time of ACLR surgery. Statistically significant elevations were seen in the lateral tibia at the superficial (p=0.03), deep (p=0.04), and full thickness (p=0.02) cartilage defects. T1rho relaxation times were also seen to increase as severity of arthroscopic lesion increased in the superficial and deep regions of the knee. This leads to the conclusion being drawn that T1rho is more sensitive than arthroscopy when viewing small cartilage lesions at time of ACLR 121. The increase in lesions experienced by the lateral compartment is not surprising when bearing in mind the shear and rotational component that is experienced at the time of ACL injury and the resulting apoptosis of chondrocytes 9. The use of T1rho has also been helpful in illustrating the damage to the cartilage in relationship to the presence of bone marrow lesions (BML). In research conducted by Bolbos et al., the knee joint of 16 patients with concurrent ACL tear and 15 healthy controls was compared via use of T1rho. BMLs were present in all of 23

33 the subjects. The lesions experienced were distributed so 81% of patients had BML present on the lateral tibia, 56% had BML present on the lateral femoral condyle, and 44% had BML to both regions. After T1rho imaging, the results were that cartilage values in the cartilage overlaying the BML was significantly increased over the lateral tibia, (47.15ms ±12.96ms (p=0.002) when compared to the control of uninjured cartilage 122. Abnormal tibiofemoral kinematics following ACLR have been associated with increased cartilage degradation 25,123. In the study by Haughom et al., 11 subjects had MRI images acquired at 18 months post-aclr surgery. T1rho relaxation times were significantly increased in the general medial femoral cartilage with injured knees having a mean T1rho relaxation time of ms and with healthy knees demonstrating a mean relaxation time of ms and a p value of This difference was more pronounced when investigators looked specifically at the weight-bearing portion of the medial femoral cartilage, with the cartilage-injured knees demonstrating a mean T1rho relaxation time of 42.2±5.9ms, while healthy knees presented with a mean T1rho relaxation time of ms, with the resulting p being equal to In measuring anterior tibial translation(att), there was a statistically significant increase in the T1rho relaxation times for those patients categorized as having abnormal ATT, suggesting that there is a possible link between altered kinematics after ACLR and early damage to the cartilage. 24

34 Chapter III METHODS Participants All participants were between years of age and were recruited to the study within 14 days of sustaining an ACL injury. Recruitment occurred upon initial presentation at an orthopedic clinic. Prior to inclusion into the study, an orthopedic physician confirmed ACL rupture via clinical exam and anatomical MRI. Measurements of the variables of interest were completed at 6 months post-aclr. We excluded females who were currently pregnant or planning on becoming pregnant within the course of the study, patients who had a prior diagnosis of inflammatory arthritis, surgery consisting of the reconstruction of multiple structures within the injured knee, or those declining to undergo ACLR. Subjects who exhibited the presence of a cardiac pacemaker, cochlear implant, clinical hypertension, claustrophobia, hepatic diseases or seizures were also excluded. Contact and scheduling of participants was completed via phone and correspondence by study personnel. Follow up visits were completed at the Sports Medicine Research Lab (SMRL) on the campus of the University of North Carolina at Chapel Hill. All participating subjects signed the appropriate informed consent form 25

35 that was approved by the Institutional Review Board at the University of North Carolina at Chapel Hill. ACLR and Therapeutic Rehabilitation All participants received a patellar tendon autograft performed by one of the three orthopedic surgeons participating in the study. Following the completed ACLR surgery, study participants were referred to either a licensed physical therapist or athletic trainer for a supervised rehabilitation program. This program began during the first week post-aclr and was deemed complete when the patient was able to return to activity. Procedures Quadriceps Strength Measurement Isometric quadriceps strength was tested at 6 months post-aclr using a HUMAC Norm dynamometer (Computer Sports Medicine Inc., Stoughton, MA). The variable of interest was quadriceps MVIC in both the ACLR limb and contralateral limb. The order of limbs being tested was selected randomly (ACLR vs. contralateral). The subject was seated in the HUMAC and positioned in 85 degrees of hip flexion and 90 degrees of knee flexion 31. The adjustable straps on the dynamometer were then used to secure the pelvis and torso of the test subject. This, coupled with the instruction for the subject to maintain the position of arms crossed in front of the chest, helped isolate the generation of force to the quadriceps musculature 124. After confirming that the axis of rotation for the lever arm would pass 26

36 through the middle of the tibiofemoral joint, the lever arm was secured to the leg at 3 cm above the ankle mortise. Participants were acclimatized to the testing procedure through the use of a progressive warm-up of isometric contractions 31. The subjects were instructed to kick out into the lever arm while attempting to reach a given percentage of their perceived maximum effort 124. Participants maintained each contraction for 2 seconds at 25%, 50%, and 75% of maximal effort 125. Following the warm-up, the participants performed 3 to 5 maximal voluntary isometric contractions, spaced 60 seconds apart until the peak torque in the limb being tested was within 10% of the previous trial in two consecutive trials 31. The torque produced during the three highest trials was averaged and used to set a target torque threshold for test trials. Two maximal effort tests were completed in which the torque met or surpassed the torque threshold. The torque signal was sampled at 2000Hz and low pass filtered at 50 Hz (zero-phase shift, fourth-order Butterworth) 31. The maximum torque produced in these two trials was normalized to body mass and averaged as the variable of interest for quadriceps strength. The limb symmetry index (LSI) for quadriceps strength was calculated by dividing the injured limb by the uninjured limb. Magnetic Resonance Imaging of the Articular Cartilage Magnetic Resonance Acquisition T1rho MRI images were sampled using a Siemens Magnetom TIM Trio 3T scanner with a 4-channel Siemens large flex coil (516 mm 224 mm, Siemens, 27

37 Munich, Germany). Participants arrived at our biomedical-imaging center 30 minutes prior to the scan and remained seated to unload the knee cartilage prior to the scan. The injured knee was scanned prior to the contralateral knee. For imaging, we used a T1rho prepared three-dimensional Fast Low Angle Shot (FLASH) with a spin lock power at 500 Hz, five different spin lock durations (40, 30, 20,10, 0 ms) and a voxel size of 0.8 mm x 0.4 mm x 3 mm (field of view =288 mm, slice thickness = 3.0 mm, TR = 9.2 ms, matrix, gap = 0 mm, flip angle = 10 degrees, echo train duration time = 443 ms, phase encode direction of anterior/posterior). Articular Cartilage Segmentation A single investigator manually segmented the tibiofemoral articular cartilage on the 0ms spin lock duration T1rho image using the ITK Snap software. A musculoskeletal radiologist confirmed anatomical accuracy of segmentations. The weight-bearing regions of medial and lateral femoral condyles and medial and lateral tibial plateaus were each identified and sub-sectioned into 3 regions of interest (ROI) based on the representation of the meniscus in the sagittal plane. The femoral condyles were segmented anterior to posterior by identifying the weight-bearing portions of the cartilage via their contact and positioning relative to the meniscus. The first ROI (MFC 1/LFC 1) comprised of the portion of the cartilage superior to the region demarcated by the borders of the anterior horn of the meniscus. The second ROI (MFC 2/LFC 2) comprised of the cartilage superior to the zone between the anterior horn of the meniscus and the posterior horn of the 28

38 meniscus. The third ROI (MFC 3/LFC 3) comprised the cartilage superior to the posterior horn of the meniscus 80. The tibial plateaus were segmented anterior to posterior by identifying the cartilage in relationship to the position of the meniscus. The first region of interest (MTC 1/LTC 1) comprised of the portion of the cartilage inferior to the region demarcated by the anterior horn of the meniscus. The second region of interest (MTC 2/LTC 2) comprised of the cartilage inferior to the zone between the anterior horn of the meniscus and the posterior horn of the meniscus. The third region of interest (MFC 3/LFC3) comprised the cartilage inferior posterior horn of the meniscus 80. T1rho Relaxation Time Quantification Voxel by voxel T1rho relaxation times were calculated from a five-image sequence created with a MatLab program (MatLab R2014b [8.4.0] MathWorks, Natick, MA, USA) using the following equation: S(TSL) = S0 exp(-tsl/t1rho). In this equation S corresponds to signal, TSL is the length of the spin-lock time, S0 is signal intensity when TSL equals zero, and T1rho is the T1 relaxation time in the rotating frame. The segmented T1-weighted MRI image was overlaid onto the calculated T1rho image to determine T1rho relaxation times for the above ROIs. Mean T1rho relaxation times were extracted for each ROI and used for analyses. Greater T1rho relaxation times were interpreted as being associated with lesser proteoglycan density. 29